1. Field of the Invention
This invention belongs to the field of pharmaceutical chemistry, and provides a series of new intermediates for the synthesis of antibiotically active cephalosporin compounds and other substances. The new compounds are exomethylenecephams, wherein the side chain at the 7-position of the cephalosporin nucleus is in the .alpha. configuration, rather than the .beta. configuration of natural cephalosporins.
2. State of the Art
Exomethylenecephams have long been known in pharmaceutical chemistry, and have long been used as convenient intermediates. See, for example, the article by Chauvette and Pennington, J. Org. Chem 38, 2994 (1973), where the synthesis of such compounds was discussed.
Exomethylenecephams wherein the side chain at the 7-position is in the .alpha. configuration have not heretofore been available, because the accepted procedures for epimerizing the compounds changed the exomethylenecepham to a 3-methylcephem. The known epimerizations of the cephalosporin and penicillin side chain take place in the presence of strong bases; see, for example, Flynn, Cephalosporins and Penicillins, Academic Press, New York, 1972, pages 105-19. For example, see page 2996 of the Chauvette and Pennington article, where treatment with a strong base is shown to convert an exomethylenecepham to the 3-methylcephem.